Soluble manganese may be introduced into an aqueous system in a number of ways, including its presence in the feed or makeup water or by addition to the system as a component of a corrosion inhibition treatment. Such aqueous systems may also be subject to halogenation processes to control microbiological growth. In the presence of halogen species in water, soluble manganese generally is oxidized to insoluble higher-oxidation state species, for instance MnO.sub.2. This can result in discoloration of the water or staining, fouling due to manganese deposits, and in those instance where manganese is a component of a corrosion inhibition treatment, the depletion of soluble manganese available for corrosion inhibition treatment activity.
Soluble manganese is generally believed to be manganese in the form of its manganous ion, which is in its second oxidation state, as Mn.sup.+2, generally referred to as "manganese (II)" or "Mn (II)". Soluble manganese, as this term is used herein, does not exclude other forms of manganese that may be dissolved or soluble in a given aqueous system. The criterior for "soluble manganese" employed below is that detectable by atomic absorption in solutions that have been filtered through 0.45 micron Millipore filters, and the amount of such soluble manganese is generally expressed in terms of concentration thereof, typically in ppm. While this pore size was chosen for convenience, it was observed that filtration of sample solutions through filters of successively small poor size (0.45, 0.10, 0.025 micron) did not significantly reduce the concentration of soluble manganese determined thereafter by atomic absorption.
In subsequent discussions, the term "halogen species" refers to those forms of halogen as they exist in aqueous systems, including, but not limited to, hypohalous (HOBr, HOCl) and hypohalite salts (M(OC1).sub.2, M(OBr).sub.n where M=Na, Ca, K, Li, and n=1,2) as they exist in equilibrium. Such species may result from the introduction of halogen in any of several forms, including, but not limited to, gaseous chlorine, sodium hypochlorite solutions (bleach), inorganic bromide salts in contact with chlorine-containing oxidants, or solid calcium hypochlorite.
The phrase "stabilization of soluble manganese" as used herein means the reduction of manganese deposits or precipitates formed in situ in an aqueous system in the presence of a halogen species, regardless of the form of such manganese deposits or precipitates, and regardless of the mechanism by which such deposits or precipitates are prevented or reduced. The stabilization of soluble manganese demonstrated below may ensue because, in the present process, manganese (II) is not oxidized to insoluble manganese species, such as MnO.sub.2, or the mechanism may be in whole or part other than prevention of Mn (II) oxidation. The mechanism may be one of inhibition of incipient precipitate, and/or solubilization other than by preventing oxidation, and/or other mechanisms not yet determined in the art. Hence the form of the stabilized manganese is not necessarily the Mn (II) ion.